An optical coupling device such as a photocoupler is provided with a light emitting portion and a light receiving portion. The light emitting portion is provided on an input side and the light receiving portion is provided on an output side. An optical signal generated at the light emitting portion is received by the light receiving portion, and a signal converted into an electric signal is output from the light receiving portion. The light receiving portion is provided with an amplifier such as a differential amplifier and an inverting amplifier.
When a trans-impedance amplifier (TIA) which is an inverting amplifier is used as an amplifier of an optical coupling device, the device can be influenced by power source noise easily. In order to suppress the influence of power source noise, a dummy trans-impedance amplifier and a dummy photodiode are provided. A photodiode occupies relatively large area in a semiconductor chip which is provided in an optical coupling device. Accordingly, when a dummy photodiode is provided in an optical coupling device, it caused a problem that an occupation area of a semiconductor chip is difficult to be reduced.